Although one kind of impurity is alone referred to, it is sufficiently plain, from the principle laid down, that believers
are generally exhorted to chastity; for, if the Law be a perfect rule of holy living, it would be more than absurd to give
a license for fornication, adultery alone being excepted. Furthermore, it is incontrovertible that God will by no means approve
or excuse before this tribunal, what the common sense of mankind
declares to be obscene; for, although lewdness has everywhere been rampant in every age, still the opinion could never
be utterly extinguished, that fornication is a scandal and a sin. Unquestionably what Paul teaches has been prevalently received
from the beginning, that a good life consists of three parts, soberness, righteousness, and godliness, (Titus 2:12;) and the soberness which he commands differs not
from chastity. Besides, when Christ or the Apostles are treating of a perfect life, they always refer believers to the
Law; for, as it had been said of old by Moses, “This is the way, walk ye in it;”
5959 The quotation is not from the writings of Moses, but an accommodation from Isaiah 30:21.
Christ confirms this,

and Paul corroborates it, “He that loveth another hath fulfilled the Law,” (Romans 13:8,) whilst they constantly pronounce a curse against all fornicators. It is not worth while to quote the particular passages
in which they do so. Now, if Christ and the Apostles, who are the best interpreters of the Law, declare that God’s Law is
violated no less by
fornication than by theft, we assuredly infer, that in this Commandment the whole genus is comprehended under a single species. Wherefore, those have done nothing but betray their disgraceful ignorance, who have sought to be praised for their acuteness
on the score of their ridiculous subtlety, when they admitted that fornication is indeed condemned with sufficient clearness
and frequency in the New Testament, but not in the Law. For, if they had reasoned justly, inasmuch as God
is declared to have blessed marriage, it must at once be concluded, on the contrary, that the connection of male and female,
except in marriage, is accursed. This is the argument of the author of the Epistle to the Hebrews, where he contrasts two
opposite things;

“Marriage (he says) is honorable in all, and the bed undefiled; but whoremongers and adulterers God will judge.”
(Hebrews 13:4.)

So also, when God forbids the priest to marry a harlot, (Leviticus 21:14,) the manifest impropriety of fornication is declared; and, if it was unlawful for the daughters of Israel to be harlots,
(Deuteronomy
23:17,) the same reasoning applies necessarily to males. Nor has Hosea taken that reproof from anywhere else but the Law? “Whoredom
and wine take away the heart.” (Hosea 4:11.) Thus, when the Prophets metaphorically condemn the corruptions of their nation, they do not always use the same; word as
Moses here does, נפ, naaph, but compare them to fornications, whereas, if fornication were lawful in itself, this metaphor would be altogether inappropriate.
Hosea was commanded to take a harlot for a wife, (Hosea 1:2;) no mention is made of adultery, and still the shame and baseness
of the people is thus condemned. Who, then, would say that fornication is free from sin, since God brands it with no ordinary
mark of ignominy? But if any should pertinaciously contest this, let him accuse Paul of error, who bears witness that an example
is set before us in the Law, that we should. not “commit fornication as some of them committed, and fell in one day three-and-twenty
thousand.” (Numbers
25:9; 1 Corinthians 10:8.) Surely, if they had not transgressed the Law, so horrible a vengeance would not have overwhelmed them. If any should object
that the crime of idolatry was mixed up with it., still the declaration of Paul remains untouched, that God was the avenger
of fornication in this infliction of punishment, which would not accord,
unless it were a transgression of the Law. And in truth, where, as recorded by Luke, (Acts 15:20,) the Apostles in their decree prohibit fornication amongst the Gentiles, the reason is at the same time added, that “Moses
is read in the synagogues.” Now, if it were not a vice opposed to the Law, no offense would have hence arisen.

We have already explained why, under this word adultery, every impure lust was condemned. We know how unbridled was the licentiousness
of the Gentiles; for, although God never suffered all shame to be extinguished together with their purity, still respect for
what was right was in a manner stifled, so that they evaded the grossness of the sin by ribaldry and scurrilous jests. At
any rate, the doctrine of Paul was by no means understood,
that those who indulge in whoredom “sin against their own body.” (1 Corinthians 6:18.)

Since, then, the minds of all men were stupified by indulgence, it was needful to arouse them by declaring the atrocity of
the sin, that they might learn to beware of all pollution. Nor are unbridled lusts only here condemned, but God instructs
His people to cherish modesty and chastity. The sum is, that those who desire to approve themselves to God, should be pure
“from all filthiness of the flesh and spirit,” (2 Corinthians 7:1;) nor can we doubt but that Paul in these words would interpret the law, as he elsewhere exhorts,

“that everyone should possess his vessel in sanctification and honor; not in the lust of concupiscence, even as the Gentiles
which know not God.” (1 Thessalonians 4:4, 5.)

59 The quotation is not from the writings of Moses, but an accommodation from Isaiah 30:21.